The required ignition timing for an internal combustion engine is different, depending on various conditions such as driving state, air fuel ratio of an air-fuel mixture, etc. In order to satisfy such required ignition timing, the internal combustion engine is provided with an ignition timing control unit. There are several known types of ignition timing control units. They include, for example, a centrifugal ignition timing control unit and a vacuum ignition timing control unit which mechanically control the ignition timing by directly introducing with transmission means ignition timing control factors such as the number of engine revolutions (engine speed), inlet pipe pressure, and the like, and an electronic ignition timing control unit which electronically controls the ignition timing by introducing ignition timing control factors such as the number of engine revolutions, inlet pipe pressure, and so forth using detection devices producing electric signals.
The electronic ignition timing control unit usually effects control stabilizing the number of idle rotations in order to maintain the number of engine revolutions to a predetermined number of idle rotations at the idle driving time of the internal combustion engine. This control for stabilizing the number of idle rotations is effected by implementing a spark advance or a spark delay from a specified ignition timing when the actual number of engine revolutions varies from a predetermined number of idle rotations due to fluctuation of the air-fuel ratio or the like during the idle driving of the internal combustion engine. In particular, when the actual number of engine revolutions drops below the predetermined number of idle rotations, the ignition timing is controlled to be spark advanced by about 1.degree.-2.degree.. On the other hand, when the actual number of engine revolutions exceeds the predetermined number of idle rotations, the ignition timing is controlled to be spark delayed. By this, the number of engine revolutions is maintained substantially at the predetermined number of idle rotations during the idle driving time of the internal combustion engine.
In this way, when the control for stabilizing the number of idle rotations is performed by the electronic ignition timing control unit, if initialization of the ignition timing during the idle driving time of the internal combustion engine is to be performed as in the centrifugal ignition timing control device and the vacuum ignition timing control device, the ignition timing fluctuates within a range of .+-.2.degree., which makes it difficult to perform the initialization.
In view of the above, another known approach is to provide a fixed ignition switch serving as a fixed ignition timing command signal input arrangement for inputting a fixed ignition timing command signal. This fixed ignition switch is turned on to input the fixed ignition timing command signal, thereby stopping the control to stabilize the number of idle rotations and causing the ignition timing to be controlled to be the fixed ignition timing. By this, the ignition timing can be controlled during maintenance to be the fixed ignition timing by turning on the fixed ignition timing switch and, in the state where the ignition timing is controlled to be the fixed ignition timing, the initialization of the ignition timing is performed during the idle driving time of the internal combustion engine.
However, if turning off of the fixed ignition timing switch is overlooked by careless mistake or the like after initialization of the ignition timing during the idle driving time by switching on of the fixed ignition switch, the vehicle subsequently runs in a state where the ignition timing is controlled to be the fixed ignition timing. As a consequence, since the fixed ignition timing is a very late ignition timing with respect to the ignition timing normally required by the internal combustion engine, there occurs a disadvantage in an internal combustion engine which includes an exhaust emission control device, for example in that catalyst is eluted, thus resulting in deterioration of the function of the emission control device.
It is therefore an object of the present invention to provide an ignition timing alarm device for an internal combustion engine which is capable of avoiding deterioration of the function of the catalyst which occurs when the vehicle runs at a speed exceeding a preset speed in a state where the ignition timing is controlled to a fixed ignition timing in order to perform initialization of the ignition timing during idle driving time of the internal combustion engine.